In the paving industry, hot asphalt is commonly transported to paving sites in dump trucks. The trucks receive hot asphalt from an asphalt mechanism located at an asphalt plant and deliver it to paving machines located at the paving sites. Modern paving machines have the ability to lay down hot asphalt very rapidly. Because of this, a large number of dump trucks is required to keep a paving machine supplied with asphalt, especially when the machine is located at a paving site remote from the asphalt plant.
As the number of trucks employed to transport hot asphalt to paving machines increases, a number of problems arise. For example, delays caused by traffic problems and the like are magnified when a large number of trucks are involved. Also, the logistics of truck maintenance increases greatly. Finally, it is more difficult to keep track of and control over a large number of trucks. Thus, it is highly desirable to reduce the number of trucks employed in an asphalt supply operation.
Heretofore, attempts to reduce the number of trucks required to supply asphalt to paving machines have centered around the design and use of large capacity dump trucks for transporting hot asphalt. Large capacity dump trucks have not gained wide acceptance for use in transporting asphalt because the use of such trucks results in several problems. For example, asphalt supply trucks must be operated in such a manner as to feed the asphalt gradually into the paving machines. When dump trucks are used to supply asphalt, this is accomplished by slowly raising the bed of the truck as the truck moves forward ahead of the paving machine. During such a process, if the dump truck and the paving machine become separated, asphalt is dumped onto the ground ahead of the paving machine. In such an event, the asphalt must be shoveled away from the path of the paving machine before more asphalt can be laid down. Obviously the larger the capacity of the dump truck the greater the shoveling problem is whenever a separation occurs.
Another problem that results from the use of large capacity dump trucks involves the tendency of asphalt to form into clumps or batches. These clumps tend to remain in the bed of a dump truck as it is raised and to then fall suddenly through the rear of the truck into the paving machine that is receiving asphalt from the truck. When this occurs, the paving machine forms waves or ridges in the pavement being laid down. Also, when large clumps fall from a dump truck, the truck often becomes dangerously unbalanced.
Yet another problem that arises from the use of large dump trucks relates to overhead obstructions such as wires, trees, viaducts, etc. Asphalt cannot be delivered to a paving machine from a dump truck except by raising the bed of the truck. When an overhead obstruction prevents the raising of the bed, other means for delivering asphalt to the paving machine must be found.
A very critical problem involving the use of large capacity dump trucks to transport results from the tendency of asphalt to flow from the rear or bottom of a dump bed first and to remain in the front or top of the bed as the bed is raised. Most large capacity dump trucks have a relatively long dump bed. The presence of asphalt in the front or top of a long dump bed as the bed is raised results in a very marked tendency of the truck to tip over. This problem is so acute that large capacity dump trucks are seldom used to transport asphalt to paving sites having any appreciable slant or bank.
The co-pending application of Robert D. Plant filed Aug. 22, 1969, Ser. No. 852,350, now U.S. Pat. No. 3,608,446, relates to a material delivery system in which hot asphalt is transported to paving machines in large capacity semi-trailers. Each trailer is provided with a conveyor system for moving the asphalt from the trailer to a paving machine. The trailers are not dumped and, accordingly, the problems of asphalt clumping and truck overturning experienced in the use of large capacity dump trucks are eliminated. Operation of the trailer is controlled from the paving machines that receive the asphalt. This assures both delivery of the asphalt at the proper rate and immediate termination of delivery upon the separation of the trailer and paving machine.
The above-identified co-pending application of John H. Holland relates to an improvement over the material delivery system disclosed in the above-identified application of Robert D. Plant. In the improved version of the system, the movement of asphalt out of the trailers is facilitated by spraying the trailers with lubricating oil before they are loaded with asphalt. An asphalt supporting beam is positioned above and parallel to the conveyor of each trailer. The beam prevents excessive asphalt packing in the trailer without hindering the unloading of asphalt.
The improved version of the system is further characterized in that the operation of the conveyor of each trailer is controlled by a valve mounted on the trailer. The valves are positioned on the trailers for actuation by prods mounted on the paving machines. This permits both control of the unloading of the trailers from the paving machines and the unloading of the trailers in situations where no prod is available.
It will be appreciated that many of the problems that are involved in the transportation of hot asphalt also arise in the transportation of other paving materials, such as slip-form concrete, etc. One additional problem that is encountered in the delivery of slip-form concrete and similar materials is the necessity of thoroughly cleaning the delivery vehicles after each use. The present invention relates to an embodiment of the improved material delivery system disclosed in the above-identified application of John H. Holland that is especially adapted to the delivery of slip-form concrete, and the like.